1. Field of the Invention
The present invention relates to a digital signal recording apparatus, particularly, to processing at the start and the end of recording.
2. Related Background Art
A digital video tape recorder (VTR) for recording an image signal onto a magnetic tape as a digital signal and for reproducing the digital signal therefrom is conventionally known. Recently, a DV format has been proposed by HD Digital VCR Conference as a digital VTR format having the specifications of consumer-use digital VCRs.
According to the DV format, the following two specifications are defined: SD Specifications (hereinafter, referred to as a SD format) for recording an image signal under NTSC standards on 10 tracks per frame; and SD High Compression Specifications (hereinafter, referred to as a SDL format) for recording an image signal on 5 tracks per frame.
In the SD format, besides image signals, various additional information, which is called system data, is recorded.
The system data includes pack information consisting of 5-byte data, ID information contained in an ID portion of each sync block and the like.
The pack information includes: a time-code indicating recording date and time and a frame; a video source and an audio source for accurately reproducing images and sounds, respectively; a video source control indicating the sort of images (a motion image and a static image), and the like.
The ID information includes a track pair number, 1-bit pilot frame information and the like. The track pair number increases from 0 to 4 in a sequential order every three tracks, assigning the track pair number 0 to the head of 10 tracks on which an image signal of one frame is recorded. The 1-bit pilot frame information indicates a frequency (f1 or f2) of a pilot signal recorded on the initial track of 10 tracks on which an image signal of one frame is recorded in the SD format.
The position where the system data to be recorded is also defined in the format. For example, a video source control pack is recorded in a VAUX region on a track. Within each track, the video source control pack is alternately recorded in a sync block numbered 19 and a sync block numbered 156.
The contents of system data recorded in an AAUX region and the VAUX region on an even-numbered track differ from those on an odd-numbered track.
The additional information is also recorded in the SLD format. The contents of the time-code vary every five tracks on which a 1-frame image signal is recorded. As in the SD format, the track pair numbers 0 to 4 recur every 10 tracks, i.e., two frames in the SLD format. For the pilot frame, the numbers 1 and 0 alternately repeat every 10 tracks.
As described above, in the case of recording in the SDL format, if the recording is terminated at the time when data for one frame is recorded, the system data that recurs every two frames in the SDL format is not sometimes completely recorded.
As a result, when the recorded portion is reproduced, the system data that repeats in a cyclic manner every two frames cannot be accurately obtained, which may result in the disturbance of the reproduced images and sounds.
In such a digital VTR, a technique for recording a new image signal so as to be continuous to the-previously recorded scene on a tape on which image signals are already recorded in the SD format, called halfway recording, is known.
In the case where halfway recording is to be performed, with a direction to start the recording in a recording temporary stop state, the feeding of a magnetic tape is first started to reproduce signals. The track at the head of a frame is detected every 10 tracks. The recording is started from the initial track, so that the previously recorded image and a newly recorded image can be continuously reproduced.
As described above, in the case where the halfway recording is started from the initial track of the tracks on which a 1-frame image signal is recorded in the same manner as in the SD format, onto the tape on which image signals are already recorded in the SDL format, there arise the following problems.
As mentioned above, the contents of the system data in the odd-numbered tracks differ from those in the even-numbered tracks. Moreover, since an image of one frame is recorded on five tracks in the SDL format, the track from which the recording is started may be either an odd-numbered track or an even-numbered track.
Therefore, in the case where the halfway recording is performed, it is necessary to detect in advance whether the track from which the recording is to be started is an odd-numbered track or an even-numbered track. Depending on the result of detection, it is required to arrange the system data and modify the recording position.
For the halfway recording, however, whether the track from which the recording is to be started is an odd-numbered track or an even-numbered track can be recognized only immediately before the recording start position. Thus, changing the recording processing for the system data depending on the recording start track will extremely increase the burden on the apparatus.
Likewise, if the halfway recording is started from the track which is not the head track within the 10 tracks on which data for two frames is recorded, among the system data, the contents of data which recurs every two frames in the SDL format are not correspondent to the system data of the portion immediately before the start of halfway recording. As a result, image signals cannot be finely reproduced in the portions before and after the halfway recording.